A typical LCD display for a computer, hand held device, television or other common electronic device comprises a light source for providing a source light, filters for transmitting primary colors of the source light, and a light modulator for selectively modulating the transmission of the source light through the filters. The light source in typical modern displays comprises solid-state emitters (such as LEDs, lasers, or OLEDs) and possibly light converting materials such as phosphors and quantum dots. The filters are configured to transmit primary colors, which are typically, blue, green and red, and are usually arranged in pixels, in which each pixel comprises filters for transmitting each of the primary colors. The light modulator is commonly an electrically-controlled liquid crystal. Such displays and their components are well known in the art.
Of particular interest herein is the emission of the blue primary color, which has a peak emission around 450-480 nm. FIG. 1 shows the white spectra emitted by the displays of two phones, an Apple iPhone (LCD with LED source) and a Samsung Galaxy (OLED screen), with a strong blue primary providing a good color gamut and high efficiency. However, the high level of blue light in these displays is a cause of concern due to its impact on the circadian cycle of the user.
Applicants have discovered that a spectrum can be configured to appear substantially white, despite a substantial absence of blue radiation, as described in Application U.S. Ser. No. 14/996,143. For simplicity, such spectra is referred to herein as blue-free. Blue-free emitters are desirable due to their reduced impact on the human circadian cycle, which is important for instance, in the evening before going to sleep.
Despite the advantages of blue-free emitters, the lack of blue radiation can be problematic in display devices. First, blue pump LEDs are preferred to excite wavelength-converting materials having a preferential absorption in the blue range. Second, the absence of blue radiation may negatively impact the color gamut. Third, the physical configuration of common displays may not be compatible with the presence of violet emitters.
Therefore, there is a need for a display system that is blue free, yet provides a good color gamut with good performance. The present invention fulfills this need among others.